Hi Hans,
On Fri, Jun 15, 2018 at 4:09 PM Hans Verkuil <hverkuil@xxxxxxxxx> wrote:
>
> On 04/06/18 13:46, Hans Verkuil wrote:
> > From: Hans Verkuil <hans.verkuil@xxxxxxxxx>
> >
> > Add initial media request support:
> >
> > 1) Add MEDIA_IOC_REQUEST_ALLOC ioctl support to media-device.c
> > 2) Add struct media_request to store request objects.
> > 3) Add struct media_request_object to represent a request object.
> > 4) Add MEDIA_REQUEST_IOC_QUEUE/REINIT ioctl support.
> >
> > Basic lifecycle: the application allocates a request, adds
> > objects to it, queues the request, polls until it is completed
> > and can then read the final values of the objects at the time
> > of completion. When it closes the file descriptor the request
> > memory will be freed (actually, when the last user of that request
> > releases the request).
> >
> > Drivers will bind an object to a request (the 'adds objects to it'
> > phase), when MEDIA_REQUEST_IOC_QUEUE is called the request is
> > validated (req_validate op), then queued (the req_queue op).
> >
> > When done with an object it can either be unbound from the request
> > (e.g. when the driver has finished with a vb2 buffer) or marked as
> > completed (e.g. for controls associated with a buffer). When all
> > objects in the request are completed (or unbound), then the request
> > fd will signal an exception (poll).
> >
> > Signed-off-by: Hans Verkuil <hans.verkuil@xxxxxxxxx>
> > Co-developed-by: Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxx>
> > Signed-off-by: Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxx>
> > Co-developed-by: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
> > Co-developed-by: Alexandre Courbot <acourbot@xxxxxxxxxxxx>
> > ---
> > drivers/media/Makefile | 3 +-
> > drivers/media/media-device.c | 14 ++
> > drivers/media/media-request.c | 421 ++++++++++++++++++++++++++++++++++
> > include/media/media-device.h | 24 ++
> > include/media/media-request.h | 326 ++++++++++++++++++++++++++
> > 5 files changed, 787 insertions(+), 1 deletion(-)
> > create mode 100644 drivers/media/media-request.c
> > create mode 100644 include/media/media-request.h
> >
>
> <snip>
>
> > diff --git a/include/media/media-request.h b/include/media/media-request.h
> > new file mode 100644
> > index 000000000000..8acd2627835c
> > --- /dev/null
> > +++ b/include/media/media-request.h
> > @@ -0,0 +1,326 @@
>
> <snip>
>
> > +/**
> > + * struct media_request - Media device request
> > + * @mdev: Media device this request belongs to
> > + * @kref: Reference count
> > + * @debug_str: Prefix for debug messages (process name:fd)
> > + * @state: The state of the request
> > + * @updating_count: count the number of request updates that are in progress
> > + * @objects: List of @struct media_request_object request objects
> > + * @num_incomplete_objects: The number of incomplete objects in the request
> > + * @poll_wait: Wait queue for poll
> > + * @lock: Serializes access to this struct
> > + */
> > +struct media_request {
> > + struct media_device *mdev;
> > + struct kref kref;
> > + char debug_str[TASK_COMM_LEN + 11];
> > + enum media_request_state state;
> > + refcount_t updating_count;
>
> This will be replaced by unsigned int: it turns out that if CONFIG_REFCOUNT_FULL is set,
> the refcount implementation will complain when you increase the refcount from 0 to 1
> since it expects that refcount_t it used as it is in kref. Since updating_count is
> protected by the spinlock anyway there is no need to use refcount_t, a simple
> unsigned int works just as well.
It seems to be read in media_request_clean(), which can be called by
media_request_release() or media_request_ioctl_reinit() and neither
acquires the spinlock for the time of the call.
Agreed, though, that refcount_t doesn't really match what we need
updating_count here for.
Best regards,
Tomasz
